1. Field of the Invention
The present invention relates to a semiconductor substrate and, more specifically, to a semiconductor substrate formed of a single-crystal silicon carbide.
2. Description of the Background Art
Recently, a silicon carbide substrate has come to be used for manufacturing semiconductor devices. As compared with more commonly used material such as silicon, silicon carbide has wider bandgap. Therefore, a semiconductor device using a silicon carbide substrate has advantages such as high breakdown voltage and low on-resistance and, in addition, its property does not much degrade in high-temperature environment.
In order to realize a semiconductor device having superior characteristics as mentioned above, use of a silicon carbide semiconductor with reduced density of crystal defects has been proposed. By way of example, U.S. Pat. No. 7,314,520 discloses a silicon carbide substrate of which screw dislocation density is reduced to 2500 cm−2 or lower.
Even when only the defects disclosed in the prior art are reduced, however, it has been difficult to improve yield of semiconductor devices formed on the silicon carbide substrate.